It is known to employ a digital audio tape cassette in a device able to record and reproduce recorded PCM signals, a kind of digital signal, converted from analog signals including audio signals. In a conventional PCM signal record-reproduce device, a turning magnetic head is used to obtain higher recording density, and its magnetic tape is pulled out from the cassette, when it is performing recording or reproducing, and is wound on a turning magnetic drum set with the turning magnetic head.
However, a defect lies in contaminating the magnetic tape which may be stained by dust or oil adhered to one's fingers in the handling process, and thus drop-out signals exist. For this reason, it would be better to envelope the magnetic tape in a case so as to protect it from contamination.
A conventional tape cassette in the prior art is typically composed of a cassette housing assembled by an upper shell and a lower shell, a slider able to move on the outer part of the lower shell, a lid able to turn at the front end of the cassette housing, two spools able to turn in the cassette housing, each of which has a ratchet, a magnetic tape having its two ends separately fixed at each rim of the two spools, a brake having two brake portions separately engaged with the ratchets of the two spools so as to prevent the magnetic tape from unwinding, a spring set between the slider and the lower shell so as to keep the slider moving only towards the lid, a metal spring set between the brake and the upper shell so as to have the brake portions separately engaged with the ratchets of the two spools, and two refraction prisms fixedly mounted in the upper shell and formed into one element to detect movement of the magnetic tape by means of refraction.
In order to have the PCM signal record-reproduce device easily controlled by the slider, or to have the slider smoothly slide on and change its position, a lock tenon at the free end of a slider lock has two oblique surfaces. Moreover, when the slider is started, it has a tendency to slide towards closing under the force of elasticity of the spring. Thus, if the cassette housing is placed in the PCM signal record-reproduce device, the slider and the lid will be opened sequentially by the device, and performance of recording and reproducing also starts. Under such circumstances, if the cassette housing incurs impacts, the slider under the force of elasticity of the spring will unexpectedly slide over the oblique surfaces and thereby close the device accidentally. The lid will be held open by the accidentally closed slider and cannot close. In normal operation, the slider cannot close until the lid closes. This will lead to a result that the cassette housing is stuck in the PCM signal record-reproduce device and is unable to be taken out, and worse, both the magnetic tape and the device will be damaged.
Furthermore, since the free end of the slider lock has two oblique surfaces, the push the slider needs when sliding over one oblique surface is equal to the push the slider needs when sliding over the other oblique surface. This is one of the major reasons for the slider being easily closed accidentally.
If a transparent window is mounted at the upper shell, and two refraction prisms are connected at the window, there will be difficulty in mounting the prisms at a proper position in the upper shell. Thus, inaccurate refraction will result in wrong operation.
When a tape clip presses the end of the magnetic tape into a concave recess of a respective spool, the snugly coupling tape clip in the concave recess can easily break the magnetic tape, and also the tape clip can drop off axially. However, if the tape clip doesn't couple the concave recess snugly enough, the end of the magnetic tape is not tightly fixed.
When the lid opens, though its arms push and press brake drivers of the brake, the lid arms can easily drop from the brake drivers, and vice versa.
The spring is a single part, which has some trouble in assembly, particularly with the brake.
When being assembled, the brake, under elasticity of the spring, has its brake portions stretch uncontrolledly, which obstructs the assembly of the two spools.